National Water Supply and Sanitation Council
Baseline Study
Aqua Privy and Soakaway
Level:
Wet on-site system
Next component technology options
Connection of the digester to a sewer system
Description:
A toilet with a water-seal arrangement: a straight or curved chute running from the seat to below the water
level with some form of waste collection and disposal system.
Principles of operation:
After defecation, the pan requires flushing with a few litres of water. An aqua privy requires the addition of
water to keep the end of the chute submerged. Containment of waste may vary from sealed container to a
solids collection system and effluent soakaway.
Operational and institutional requirements:
Appropriate for small volumes of water and can accept domestic wastewater – generally carried by hand to
the toilet. Ensure access for mechanical emptying of contained waste, and suitable subsoil drainage (high
reliance on the soil environment in rendering the effluent harmless) and / or availability of sludge treatment
and disposal.
Costs:
Initial cost: € 90–375 (including labour and materials). Actual costs will depend on the tank volume, whether
materials are available locally and local prices. Operation and maintenance account for around 1 % of the
investment costs per year plus the amount for emptying. Because water is required for flushing the price has
to be taken into account.
Experience and comment:
International acceptance demonstrated where water used for anal cleansing and users squat. Blockages
occur through use of inappropriate anal cleansing material. Experience has seen failures due to: (1) poor
design and construction, (2) its use in areas where it is an inappropriate technology and (3) limited provision
of affordable emptying service.
Aqua privies connected to a soakaway or to sewer system are found in Zambia preferably in low-cost areas.
Experience has shown that the water seal may not always be maintained (usually because of failure or inadequacy of the water supply), so that the system suffers a relatively high risk of intermittent malfunction. The
sewered aqua privy can be considered as functionally equivalent to a sewered pour-flush toilet. The sewered
pour flush toilet is the superior system and it is also marginally cheaper. Thus aqua privy systems ordinarily
cannot be recommended as a viable sanitation option since.
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Does not require electricity.
Once constructed the toilet is permanent.
Reliable.
Several low cost options for effluent collection.
System works well where the soil is permeable and not liable to flooding or
water logging.
No separate sullage disposal required.
High potential for upgrading.
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Low construction skills needed.
Municipal involvement can be limited to design and maintenance guidelines.
Construction material locally available.
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Easy to maintain.
O&M
IMPLEMENTATION
TECHNICAL
ADVANTAGES
DISADVANTAGES
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OTHERS
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With a proper soak-away pit minimal risk to public health.
Users have convenience of conventional cistern flush toilet.
Can be installed on an individual basis.
Easily upgraded to a sewerage system by connection of the effluent pipe.
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Reliable and ample water supply from house connection required.
Water needed per flush: 2–5 litres, if a pour-flush pan or aqua privy is used.
Requires soil permeability 10-7 m/sec to dispose effluent.
If the soil has a low permeability, or if the water table is high, it may be necessary to connect the tank to a sewer system, if available.
Nearby shallow wells can not be used for drinking water supply.
Availability fails due to clogging of the soil.
Groundwater table must be about 1.0 m below soak-away pit.
Not suitable for flood prone areas.
Effluent still contains pathogens, cysts and worm eggs.
Construction of septic tank requires skilled labour.
Low effluent quality.
Expensive watertight tank is needed to maintain water seal.
Requires manufactured parts (water seals, toilet bowls).
Requires construction control.
Not suitable where water supply scarce or unreliable.
Providing reliable services for emptying the tanks, ensuring that skilled contractors are available for construction and repairs, and controlling sludge disposal.
Requires periodic desludging.
Sludge needs careful handling.
Requires septic sludge transportation and disposal.
Requires access for emptying services (collection carts or vehicles).
Since only accepts liquid waste must be connected to a flush toilet.
Large amounts of detergents or chemicals may disturb the biochemical processes in the tank.
Maintenance of water seal might be a problem (intense odour release and fly
and mosquito nuisance.
Large land requirement for effluent disposal unsuitable for high-density housing.
Effluent may contaminate groundwater.